Lets have some controversy shall we. Duke walks out of a building and see a bunch of ugly fat women dead and he says "Looks like they should of stayed in the kitchen".

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"Ever since I was a little boy, dressing up has always been...my greatest joy. But when It's time to be discreet, there is one thing you just can't beat and that's a strapless backless classical little black dress"

Duke should acquire a Dirty Harry styled revolver (the Smith and Wesson Model 29) in the western town, that is assumed to be in the game, and when you get a head shot with it he should say, "I guess you weren't feeling lucky... Punk!"

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RAWR! I'm in the Duketard Guild, because I am a lvl 70 bad ass. "Eat shit and die!"

Well you could have master chief in a secret room with an elites plasma sword up his arse and duke replies "talk about reach!".
Or how about you look under a bed and theres serious sam shivering and weeping like a lil girl and Duke says "why so serious?" before leaving him with a pipe bomb.

He in a level that looks like a castle and he see's a pour look a like of Harry Potter and he says to him when you hit the Action Button. "Keep looking at me like that, Point Dexter and watch me pull a Rabbit....Out of your Ass!"